ΔE 43.5, loose: different enough that you should pick on purpose. Ink Sepia is noticeably darker, more muted, warmer than Turquoise Ink.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 43). Ink Sepia is noticeably darker, more muted, warmer than Turquoise Ink.
The same difference applies the other way round: Turquoise Ink is noticeably lighter, more saturated, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Turquoise Ink on the colour wheel See Ink Sepia on the colour wheel
All matches: Turquoise Ink equivalents · Ink Sepia equivalents